1. Field of the Invention
The present invention relates to a throttle control device for an internal combustion engine, which is to be mounted in, for example, a supercharged-engine vehicle and a throttle control method for an internal combustion engine, paying attention, in particular, to capability of improving durability of components by devising a control method when a throttle valve is to be closed for deceleration during a high-load operation.
2. Description of the Related Art
The following turbocharger is hitherto known. Specifically, for the purpose of improving an output of an internal combustion engine (hereinafter referred to simply as “engine”), the turbocharger includes a supercharger for toting and moving a turbine by an exhaust gas, which is mounted in an intake path of the engine. In the case where the turbocharger is used, there is a fear in that a supercharging pressure disadvantageously increases more than needed when the engine is rotating at a high speed under a high load, resulting in damage to the engine.
Therefore, generally, the pressure (supercharging pressure) in the intake path of the engine is controlled at a proper level by using an exhaust bypass passage provided upstream of the turbine. Specifically, by controlling opening/closure of a wastegate valve (hereinafter referred to as “WGV”) provided in the exhaust bypass passage, the exhaust gas flowing through an exhaust path is split so that a part of the exhaust gas flows into the bypass passage to adjust an inflow amount of the exhaust gas into the turbine. In this manner, the supercharging pressure is controlled at the proper level.
In general, the WGV is driven by using a positive-pressure type actuator. The WGV has a mechanism as follows. The intake path (in particular, a portion located upstream of a throttle valve, in which the pressure increases) of the engine and a wastegate actuator (hereinafter referred to as “WGA”) are connected to each other. When the pressure in the intake path of the engine becomes larger than an atmospheric pressure, an operation of the WGA is enabled.
However, if the pressure in the intake path of the engine is not equal to or larger than a predetermined value, an opening degree of the WGV cannot be controlled. Therefore, in recent years, there has been proposed a system in which the WGA is motorized to enable the operation of the WGV as needed regardless of the pressure in the intake path.
As one of the related-art technologies described above, the following method has been proposed. Specifically, when a throttle valve is to be closed for deceleration during a high-load operation, an opening degree of the WGV is increased in accordance with the amount of closure of the throttle valve so that an increase in pressure in the intake path of the engine (hereinafter referred to as “throttle-valve upstream pressure”) is quickly reduced (see, for example, Japanese Patent Application Laid-open No. 2012-246800).
According to the related-art method disclosed in Japanese Patent Application Laid-open No. 2012-246800, when the throttle valve is fully closed or nearly fully closed during the high-load operation in which the throttle-valve opening degree is large, the WGV is nearly fully opened. In a state in which the throttle valve is fully closed, however, there still remains a problem in that the throttle-valve upstream pressure increases excessively under the effects of a pressure of a compressor which rotates integrally with the turbine rotating through inertia.
As another related-art technology to cope with the above-mentioned problem, there has been proposed a method of controlling the throttle-valve opening degree as well as the opening degree of the WGV to control an intake air amount (see, for example, Japanese Patent Application Laid-open No. 2008-297929).
However, the related-art technology described above has the following problem.
According to the related-art method disclosed in Japanese Patent Application Laid-open No. 2008-297929, in the case where the throttle-valve opening degree is controlled so that a delay is generated in an actual intake air amount when the throttle valve is closed after a deceleration command is issued, the throttle valve is not closed abruptly. Therefore, the effects of suppressing the problem of the excessively increased throttle-valve upstream pressure can be expected to be obtained. However, the throttle valve is sometimes closed abruptly depending on an operating state (see the alternate long and short dash line *5 in FIG. 5 of Japanese Patent Application Laid-open No. 2008-297929). As a result, there may still arise a problem of the excessive throttle-valve upstream pressure rise. Moreover, the throttle-valve upstream pressure is not monitored, and hence there is a problem in that the throttle-valve upstream pressure rise cannot be avoided reliably.